The present invention relates generally to a printing machine, and more particularly to an arrangement for applying ink to a pick-up roller in an ink-applying apparatus.
It is known that the thickness of the ink layer discharged from the ink reservoir must be adjusted so that ink to be applied is dosed to a predetermined value. In the known so-called wedge-type ink-applying arrangements the adjustment of the thickness of the ink layer is carried out by adjusting of the position of a doctor blade relative to the circumferential surface of the pick-up roller. The doctor blade in such arrangements is pressed against the pick-up roller by screw-setting devices whereby a gap between the roller and the doctor blade is changed. In such arrangements the individual color zones formed along the width of the ink reservoir in the region of the aforementioned gap are adjusted to a differing degree so that due to differing pressures on the doctor blade along the entire width of the reservoir a uniform ink profile can not be obtained.
Because the doctor blade is elastic and the neighboring color zones are differently adjusted by the screw devices and thus have a differing thickness they affect each other which also leads to the uneven ink layer along the width of the reservoir.
Devices for relatively accurate adjustment of ink layer in the ink-applying devices have been already suggested where dosing and supply of ink were controlled by pumps. Such construction is disclosed, for example in the Swiss patent No. 392,565. In the disclosed construction a plurality of pumps are mounted along the width of the ink reservoir which supply ink to respective friction rollers. It should be noted that with relatively high expenses, the satisfactory dosing of ink at individual color zones connected to respective sprinkling nozzles may be obtained. However, it should be recognized that the necessity of periodical changes and subsequent cleaning of all ink pumps, conduits and nozzles are considerably troublesome and lead to high expenses in utilization of the known devices. Furthermore, it is to be understood that in the known devices an individual drive is required for each discrete color zone and each individual nozzle outlet must be adjusted to a predetermined value in order to avoid changes in the ink profile. For these reasons, pumps, brushing devices, and centrifugal devices have not found general acceptance.
In order to overcome the problems experienced in the ink-applying arrangements it has been suggested to further improve ink dosing by changing nozzles in the ink reservoir. Such proposal is disclosed, for example, in the German patent No. 2,553,177.
The Swiss patent No. 561,119 discloses another modification of the ink-applying device where a slotted doctor blade is suggested which is formed with a plurality of neighboring portions operating independently from each other.
In the device, described for example in the U.S. Pat. Nos. 1,275,348 and 1,574,474, the doctor blade is formed of a plurality of descrete adjustable sliders. Such sliders disclosed, for example in the U.S. Pat. No. 3,978,788 are adjacently positioned along the whole width of the ink reservoir so that alltogether they form the doctor blade.
In order to change the position of the doctor blade each slider is provided with an electromotor coupled with a transmission and an eccentric device cooperated with the slider. The disadvantage of such construction is that all inaccuracies occured during the adjustment of the discrete sliders directly affect the ink layer to be dosed causing its deflection from a predetermined value. Moreover, due to the reduction of number of revolutions of electromotors required for operation of the eccentric devices a preliminary designed and calculated gap between the pick-up roller and the doctor blade should be further adjusted.
All this leads to the fact that the extremely accurate adjustment of the ink gaps in the ink-applying devices involves very high expenses since the once adjusted gap should be monitored and then readjusted again for a certain value of accuracy required in each individual case.
The U.S. Pat. No. 3,730,089 suggests to utilize a funnelshaped ink reservoir instead of the wedge-type ink containers. The ink within the reservoir is monitored by forming it into a vortex and then monitoring a radial dimension of the vortex. In such devices the doctor blade is formed by at least one of the longitudinal walls of the ink-reservoir.